Saturday, 15 July 2006

Interaction of Organic Manures and Granular Size of Inorganic NPK Fertilizers on Nutrient Uptake and Grain Yield of Irrigated Rice in Vertisols.

Subbaiah SV, Rama Prasad AS, Kumar RM, and Surekha K. Directorate of Rice Research, Rajendranagar, Andhra Pradesh, Hyderabad, 500030, India

In the green revolution era, intensive rice cropping with high-yielding rice varieties along with increased use of inorganic fertilizers and improved irrigation facilities have resulted in spectacular increases in crop productivity. Organic sources available for use in rice production include bulky organic manures such as Farm Yard Manure (FYM) or quick-growing green manure crops. Multilocational long-term trials in India (AICRIP trials) have shown a 50% decline in the rice yield response to nutrients, from 15 to 16 kg grain kg -1 NPK nutrients applied in the sixties and seventies to a level of 7 to 8 kg grain kg -1 NPK applied in the nineties (DRR quinquennial Review Report, 1996). Several studies have been conducted on the complementary use of organic and inorganic fertilizers in cropping systems involving rice. The objective of the present study is to evaluate effects of granular forms of N and P fertilizers in conjunction with FYM and Green Manure (GM) on grain yield and nutrient uptake in rice-rice cropping system. A field experiment was conducted with medium duration high-yielding rice cultivar Ajaya during the period 1995-96 to 1997-98 in both rabi and Kharif seasons at the Directorate of Rice Research, Rajendranagar, Hyderabad on a Vertisol. The status of available N was low (227 kg ha-1), available P was medium (33 kg P2O5 ha-1) and available K was high (587 kg K2O ha-1). The three main treatments consisted of organic manures viz., GM represented by Sesbania aculiata at 10 t/ha in situ, FYM at 10 t/ha and no manure. The 7 sub-plots consisted of different combinations of inorganic fertilizers viz., Prilled Urea (PU), DiAmmonium Phosphate (DAP), muriate of potash (MOP), Large Granular Urea (LGU), Single Super Phosphate (SSP) and Large granular Di-Ammonium Phosphate (LDAP). The combinations were PU+SSP+MOP, PU+DAP+MOP, PU+LDAP+MOP, LGU+SSP+MOP, LGU+DAP+MOP, LGU+LDAP+MOP and Control applied at two doses of NPK viz., high (120+60+40) and low (60+30+20). Grain yields in the treatments receiving inorganic manures alone were around 4000 kg ha-1 throughout the six seasons. In the main treatments, GM+NPK and FYM+NPK showed a yield advantage over NPK applied without organic manures. Over the long term, application of organic manures with NPK was beneficial in getting more yields. The gain of yield due to application of green manures was around 633 kg ha-1 (16%) in the first season and increased to more than 1438 kg ha-1 (33%) by the end of 6th season. The importance of combined use of organic manures and inorganic fertilizers in enhancing grain yields was reported earlier also (Matiwad and Sheelavantar, 1994; Singh at. al., 1990; Subbaiah et. al., 2000). At the higher dosage of NPK (120+60+40), the treatment LGU+DAP+MOP with GM followed by LGU+LDAP+MOP with FYM showed the highest cumulative yield gain of 8530 kg ha-1 and 8380 kg ha-1 over all the 6 seasons. At the low dosage of 60+30+20, GM with PU+DAP+MOP followed by FYM with PU+SSP+MOP and FYM with PU+DAP+MOP recorded highest cumulative gain of 6000 kg ha-1 , 5830 kg ha-1 and 5800 kg ha-1 respectively. In general, the total N uptake by the crop during Kharif (105.9 kg ha-1 ) was significantly lower than in rabi season (120.5 kg ha-1), whereas the total P uptake was similar (82-85 kg ha-1 )during both the seasons. With regard to the effect of total N uptake on grain yield, there was a slight advantage due to FYM in converting N uptake to grain yield in both seasons. Among the fertilizers used LGU+DAP+MOP and PU+SSP+MOP with higher doses showed more yield gain due to higher N uptake than in other combinations. At the lower dosages PU+SSP+MOP and PU+DAP+MOP are the combinations that are promising in terms of N uptake and grain yield. When the influence of N alone on grain yield was considered the b' value i.e. increase in kg of grain per each kg of increased N uptake was similar at higher and lower levels (41-43) of inorganic fertilizers during kharif. However during rabi the b value was less (23.2) at lower fertilizer levels compared to 38.2 at higher fertilizer levels indicating that other nutrients probably P and/or K or micro-nutrient(s) might be acting as limiting factor in converting N uptake to grain yield. It was concluded that large granular forms of N and P fertilizer were better than powdered and prilled forms for increasing nutrient uptake and grain yield of rice in irrigated low land soils. Addition of GM along with NPK was promising during the first three seasons while FYM along with NPK was better during later three seasons indicating long term use of FYM for better yields in rice-rice cropping systems in vertisols.

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